Color stabilization of lubricating compositions

ABSTRACT

THE DARKENING AND DISCOLORATION OF LUBRICATING GREASES AND OILS INDUCED BY THE USE OF METAL SALTS OF SUBSTITUTED DITHIOCARBAMIC ACID ARE EFFECTIVELY PREVENTED BY THE INCLUSION OF SMALL AMOUNTS OF POLY(PHENYLENE SULFIDE) IN THE LUBRICATING COMPOSITON.

United States Patent 3,630,897 COLQR STABILIZATION 0F LUBRICATING COMPOSITIONS Raymond Rohde and Andrew E. Skeen, Bartlesville, Okla, assignors to Phillips Petroleum Company No Drawing. Filed Oct. 6, 1969, Ser. No. 864,210 Int. Cl. 010m 1/32, 1/38 U.S. Cl. 25233.6 7 Claims ABSTRACT OF THE DISCLOSURE The darkening and discoloration of lubricating greases and oils induced by the use of metal salts of substituted dithiocarbamic acid are effectively prevented by the inclusion of small amounts of poly(phenylene sulfide) in the lubricating composition.

3 H NCSH Metal salts of substituted dithiocarbamic acids are useful in providing improved resistance to coking under severe engine operating conditions, as stabilizers to prevent oxidative thickening of oils and lubricants under extreme pressure conditions, and to provide other improved properties in lubricants. More specifically, these additives are polyvalent metal salts of N-aliphatic hydrocarbon substituted dithiocarbamic acids containing sufficient aliphatic carbon atoms to impart oil solubility to the molecule. These polyvalent metal dithiocarbamates are usually employed in amounts from 0.1 to 5 to percent by weight of a lubricating composition.

Unfortunately, 'with the good effects have come side effects. Most freshly formulated lubricating compositions have a light clean-looking color, a creamy appearance, which greatly improves appearance and saleability of the formulations. Lubricating compositions containing these salts, however, have shown a tendency to darken severely and quickly.

Darkening of these formulations in many instances is erroneously attributed by the consumer to old or aged materials, or, in some instances, to use of recovered or reclaimed ingredients. Further, variations between the color-appearance of separate packages is observed, even though similarly compounded and of equal quality. These factors reduce commercial acceptance of the formulations.

We have discovered that this discoloration of lubricating compositions containing metal salts of substituted dithiocarbamic acid can be effectively avoided by including minor amounts of poly(phenylene sulfide) in the formulation.

More specifically, by including small amounts of poly- (phenylene sulfide) in the lubricating composition, the shelf-life is extended, good color stability is obtained over an indefinite time, and the composition maintains a uniform clean fresh new appearance.

Therefore, it is an object of our invention to improve the shelf-life and color stability of lubricating compositions.

3,630,897 Patented Dec. 28, 1971 'ice It is a further object of our invention to prevent the agedarkening of lubricating compositions due to metal dithiocarbarnate additives in the composition.

These metal dithiocarbamate additives, and hence our color stabilizer poly(phenylene sulfide), can be employed in a wide variety of lubricating compositions or formulations. Such lubricating compositions range, for example, from motor oils, gear oils, cutting oils, to greases and to specialty lubricants. Most lubricating compositions utilize a mineral oil base such as a conventionally refined crude oil lubricating stock having a viscosity in the range of 50 to 1500 SUS at F. In addition to such natural base oils, various synthetic base oils can be used. The synthetics include polymerized olefins, copolymers ,of alkylene glycols and oxides, organic esters of polybase organic and inorganic acids, silicone polymers. Various metallic soaps are used in the formulations, particularly the grease formulations. Additives can include finely divided silica or other ingredients for a variety of purposes.

The dithiocarbamate salts used as additives can be represented by the formula:

in which the R groups represent hydrogen or organic groupings, and can be the same or dissimilar. Each R group, when other than hydrogen should have a minimum of 4 carbon atoms in the group. The R groups can be selected from alkyl, aryl, alkylaryl, cycloalkyl, and combinations thereof. Heterocyclic groupings can be utilized, including sulfur, oxygen, phosphorous, and nitrogen, where particular functions are desired. Normally, aliphatic hydrocarbon groups are employed so that each R group is an alkyl group of from 4 to about 20 carbon atoms.

Among the salts of substituted dithiocarbamic acid mentioned in the literature as additives for lubricating compositions are those of aluminum, antimony, bismuth, cadmium, chromium, cobalt, copper, iron, lead, magnesium, manganese, mercury, nickel, tin, zinc, and others.

The poly(phenylene sulfide) polymers to color-stabilize and improve the shelf-life of lubricating compositions are employed in a range of from about 0.1 to about 3 weight percent based on the weight of the total lubricating composition. We have found a range of between 0.5 and 1.5 weight percent to be quite effective, and prefer not to use over 1 percent since we find no particular increase in efffectiveness, only a slight increased cost for the final composition.

The following examples demonstrate the effectiveness of our invention, and should be considered as illustrative and not as delimiting.

EXAMPLE I Lubricating grease compositions were prepared. The grease compositions were of the same formulation with only the additives varied in accordance with the present invention.

Group 1 samples were a lubricating grease composition containing a lead diamyldithiocarbamate additive as the metal dithiocarbamate in the proportion of 2.5 percent by weight of the composition.

Group 2 samples were identical to the first group except further containing 1 weight percent of poly(phenylene sulfide) as additional additive.

Group 3 samples were identical to Group 1 except that 2.5 weight percent antimony dialkyldithiocarbamate was used as the metal dithiocarbamate.

Group 4 samples were identical to Group 3 except further containing 1 weight percent of poly(phenylene sulfide) as color stabilizer.

Both groups of samples not containing our additive, i.e., Groups 1 and 3, darkened in less than a month. Group 1 samples turned black or near-black in less than a thirty day interval. Group 3 samples turned a dark unpleasant red.

In distinction, Groups 2 and 4 containing our color stabilizer, poly(phenylene sulfide) as per our invention, all stayed clear and fresh with a bright new creamy appearance for two years and two months without color deterioration. The test was ended at that time as there was no observable deterioration of color over a very long and conclusive interval.

The lubricating composition used in the groups of samples was a mineral oil-based formation incorporating a lithium soap and a polyolefin. The mineral oil component had a viscosity of 7085 SUS at 210 F., pour point maximum 5 F., flash point minimum 430 F., fire point minimum of 480 F. The soap incorporated was a lithium l2-hydroxy stearate. Soap content was between 6 and 12 weight percent. Polyolefin content was between 5 and 6 weight percent. Nil water content. Original color a light creamy tan. Texture of the grease composition was buttery to medium fiber. The grease corresponded to the Ford body grease specification ESBM1C93A.

While other methods of producing poly(phenylene sulfide) may be used the method described in the hereinbefore referenced U.S. Letters Pat. 3,354,129 is particularly useful. The method includes reacting at least one polyhalo-substituted cyclic compound containing unsat uration between adjacent ring atoms and wherein the halogen atoms are attached to the ring carbon atoms, with an alkali metal sulfide, in a polar organic compound, at an elevated temperature. The polar compound selected will substantially disperse both the alkali metal sulfide and the polyhalo-substituted aromatic compound.

The polyhalo-substituted compounds which can be employed as primary reactants are represented by formulas given in detail in the Edmonds et al. patent. The preferred compounds are those which contain not more than 3 halogen atoms, and particularly preferred are the dihalo-substituted compounds.

A wide variety of polyhalo-substituted compounds are useful including 1,4-dichlorobenzene, 1,4-diiodobenzene, 1,4-difiuorobenzene, 2,5-dibromoaniline, 1,2,4 S-tetrabromobenzene, methyl 2-5-dichlorobenzoate, 2,5-dichlorobenzamide, 2,5-dibromothiophene, ethyl 2,4,5-trichloroacetanilide, 1-cyclohexylthio-2,5-dichlorobenzene 4,4- dibromodiphenyl, 3,4-dichlorofuran, 3,4-difluoropyrrole, 2,5-dichloropyridene, 4,8-diiodoquinoline, p,p'-dichlorodiphenyl ether, 3,3'-dichlorodiphenyl dimethylsilane, di(2-methyl-4-bromophenyl) sulfoxide, methyl di(3-ethyl- 4-chlorophenyl) phosphite 4-bromophenyl 3-n-butyl 4-chlorophenyl sulfone, 2,5-dichlorobenzene sulfonic acid, 2,6-dichloropyrazine, 4,4-bis-p-bromophenyl ether, and others as shown in the aforementioned Edmonds patent.

Alkali metal sulfides useful in the process include the monosulfides of sodium, potassium, lithium, rubidium and cesium. A particularly preferred reactant is sodium sulfide. Either anhydrous or hydrated forms of the sulfides are useful.

Polar organic compounds useful as solvents and dispersants include amides, lactams, sulfones, and the like- Examples include hexamethylphosphoramide, tetramethyl urea, N,N'-ethylenedipyrrolidone N-metl1yl-2-pyrrolidone, pyrrolidone, caprolactam, N-ethylcaprolactm, sulfolane, dimethylacetamide, low molecular weight polyamides, and the like.

Preparation of the poly(phenylene sulfide) polymers by this process is carried out by contacting reactants in a polar solvent at a temperature of from about 125 to 550 C., preferably from about 300 to 500 C. The mole ratio of polyhalo-substituted aromatic or heterocyclic compound to alkali metal sulfide should be at least 0.121 and will generally not exceed 2.0: 1. The amount of polar organic solvent or dispersant present in the reaction zone can vary widely from about to 2500 milliliters of alkali metal sulfide.

The lubricants and lubricating compositions stabilized according to our invention can be prepared by methods known to the art for formulating oils, greases, and the like.

For example, base oils and other ingredients, including our stabilizing additive poly(phenylene sulfide) are brought together in a mixing or blending vessel. For maximum mixing convenience and subsequent lubricating properties, the solid ingredients should be in a state of finely divided subdivision. The mixture is heated with constant agitation and blended at temperatures ranging from about ambient to 500 F. for a sufficient time to obtain maximum homogeneity. The blended formulation then is cooled to room temperature. If desired, the blended compositions can be packaged while in a more fluid condition due to the elevated blending temperatures and then cooled to room temperature.

Alternatively the poly(phenylene sulfide) additive can be added by blending or stirring into an already compounded formulation, heated, if necessary, to a suitably convenient blending temperature depending on the formulation consistency. Poly(phenylene sulfide) is quite heatstable to well above 500 F., so is readily blended within the suggested range without decomposition.

Our examples and discussions have pointed out a serious problem involved in the use of substituted metal dithiocarbamates in lubricating compositions, and have clearly disclosed that our invention is the solution. The use of poly(phenylene sulfide) polymers eliminates the discoloration problem.

Reasonable variations and modifications of our invention are possible within the scope of our disclosure without departing from the scope and spirit thereof as disclosed in the specification and claims.

We claim:

1. An improved color stabilized lubricating oil or grease composition containing from 0.1 to 10 weight percent of an antimony salt of a dithiocarbamic acid having the formula:

wherein each R is hydrogen or alkyl, aryl, alkylaryl, cycloalkyl, or combination thereof, and where other than hydrogen contains from 4 to 20 carbon atoms, said antimony salt tending to severely discolor said lubricating oil or grease composition, and from 0.01 to 3 weight percent of poly(phenylene sulfide) substantially stabilizing the original color of said lubricating oil or grease composition.

2.. The improved color stabilized lubricating oil or grease composition according to claim 1 wherein said poly(phenylene sulfide) has been prepared by reacting under polymerization conditions at least one polyhalosubstituted cyclic compound containing unsaturation between adjacent ring atoms and wherein the halogen atoms thereof are attached to ring carbon atoms with an alkali metal sulfide in the presence of a polar organic compound capable of substantially dispersing both said polyhalosubstituted aromatic compound and said alkali metal sulfide, at an elevated temperature.

3. The improved color stabilized lubricating oil or grease composition according to claim 2 wherein said polymerization conditions include a reaction time of from 200 to 1600 minutes, a temperature of from to 550 F., a mole ratio of said polyhalogenated ring compound to said alkali metal sulfide of from 0.1:1 to 2:1, and from 100 to 2500 ml. of said polar organic compound per mole of said alkali metal sulfide.

4. The improved color stabilized lubricating oil or grease composition according to claim 3 wherein said polyhalogenated compound is a dihalo-substituted ring compound wherein the halogen atoms thereof are selected from at least one of fluorine chlorine, bromine, and iodine, and are attached to ring carbon atoms; the said alkali metal sulfide is selected from sulfides of lithium, sodium, potassium, and rubidium; the said polar organic compound is a compound that will substantially disperse both the said polyhalogenated compound and the said alkali metal sulfide and is selected from amides, lactams, sulfones, and mixtures thereof.

5. The improved color stabilized lubricating oil or grease composition according to claim 4 wherein said dihalo-substituted ring compound is selected from p-dichlorobenzene, 4,4'-dibromodipheny1, 2,5-dibromothiophene, 4,4'-bis'p-bromophenyl ether, and 2,5-dich1orobenzene sulfonic acid; the said polar organic compound is selected from at least one of hexamethylphosphoramide, tetramethylurea N,N'-ethylenedipyrrolidorie, N-methyl-Z- pyrrolidone, pyrrolidone, caprolactam, N-ethyl caprolactam, sulfolane, dimethylacetamide, and mixtures thereof.

6. The improved color stabilized lubricating oil or grease composition according to claim 5 containing from 0.5 to 1.5 weight percent of said poly(phenylene sulfide).

7. The improved color stabilized lubricating oil or grease composition according to claim 6 wherein said composition is a mineral oil based formulation incorporating a lithium soap and a polyolefin, wherein the,

References Cited UNITED STATES PATENTS 2,825,695 3/1958 Mahoney et a1. 25233.6 3,248,325 4/1966 Graham 252---33.6 3 354,129 11/1967 Edmonds et al. 252-63] X DANIEL E. WYMAN, Primary Examiner W. H. CANNON, Assistant Examiner 

